fix(frontend): replace invalid "context" select field with "metadata" in threads.search (#2053)

* fix(frontend): replace invalid "context" select field with "metadata" in threads.search

The LangGraph API server does not support "context" as a select field for
threads/search, causing a 422 Unprocessable Entity error introduced by
commit 60e0abf (#1771).

- Replace "context" with "metadata" in the default select list
- Persist agent_name into thread metadata on creation so search results
  carry the agent identity
- Update pathOfThread() to fall back to metadata.agent_name when
  context is unavailable from search results
- Add regression tests for metadata-based agent routing

Fixes #2037

Made-with: Cursor

* fix: apply Copilot suggestions

* style: fix the lint error

frontend/src/core/threads/hooks.ts

@@ -212,6 +212,13 @@ export function useThreadStream({
     onCreated(meta) {
       handleStreamStart(meta.thread_id);
       setOnStreamThreadId(meta.thread_id);
+      if (context.agent_name && !isMock) {
+        void getAPIClient()
+          .threads.update(meta.thread_id, {
+            metadata: { agent_name: context.agent_name },
+          })
+          .catch(() => ({}));
+      }
     },
     onLangChainEvent(event) {
       if (event.event === "on_tool_end") {
@@ -528,7 +535,7 @@ export function useThreads(
     limit: 50,
     sortBy: "updated_at",
     sortOrder: "desc",
-    select: ["thread_id", "updated_at", "values", "context"],
+    select: ["thread_id", "updated_at", "values", "metadata"],
   },
 ) {
   const apiClient = getAPIClient();